The aircraft braking system of the present invention applies to all types of hydraulically applied brakes but is particularly suited for use on aircraft having hydraulically applied carbon disc brakes.
Because of their light weight, carbon disc brakes are currently being used on aircraft. A common well-known problem with carbon disc brakes is that they apply a torque reaction to an aircraft wheel which is non-linear with speed. For example, the torque reaction typically increases at low speeds even though the hydraulic pressure which actuates the brakes remains constant. As a result, in order to smoothly brake an aircraft, a pilot must constantly adjust brake hydraulic pressure, usually by a pressure control valve mechanically connected to a foot pedal by a cable.
The patent literature discloses a number of braking system patents which propose solutions to the foregoing problem. Hirzel et al, U.S. Pat. No. Re 30,763; Masclet, U.S. Pat. No. 4,138,164; Signorelli et al, U.S. Pat. No. 4,043,607; Hirzel et al, U.S. Pat. No. 4,022,513, Gentet et al, U.S. Pat. No. 3,948,569; Hirzel et al, U.S. Pat. No. 3,920,278; Booher, U.S. Pat. No. 3,711,163; and Steigerwald, U.S. Pat. No. 3,520,575 all disclose a way of regulating hydraulic pressure to compensate for a non-linear braking action. Most pertinent is Hirzel, U.S. Pat. No. 3,920,278 which discloses an automatic braking control system that enables a pilot to preselect a constant rate of deceleration, with the system adjusting hyraulic pressure to compensate for non-linear braking action. The Hirzel system includes a control dial by which one of a plurality (e.g. 5) of deceleration rates can be selected. The system maintains a constant aircraft deceleration according to that rate which is selected. The system operates automatically, independent of pilot control, until the pilot manually actuates the brake pedals which switches off automatic control.
A disadvantage to the above automatic braking system is that it provides no means for separately controlling individual wheel trucks on the landing gear of the aircraft. The landing gear on large aircraft typically includes two wheel trucks each of which is located laterally opposite the other. Each wheel truck is separately controlled by a brake pedal and therefore can be braked separately. By braking one truck at a greater or lesser rate than the other, a pilot can use the brakes as a means for steering the aircraft when landing. The above system automatically brakes each truck at the same constant deceleration rate. Thus, if the pilot wishes to use the brakes for steering control he cannot use the automatic braking system. As a consequence, the pilot must then contend with the above mentioned non-linear braking action. If the pilot chooses not to use the brakes for steering purposes, leaving braking to the automatic system, then all steering must be done by operation of the rudder which is not as effective a means for steering, especially at low speeds.
Many aircraft do not have automatic braking systems. All braking is done by the pedals and the non-linear brake response is always a problem.
Another disadvantage to the above described automatic braking system is that the pilot cannot change the rate of deceleration when under automatic control. The pilot preselects a rate of deceleration and the system continues to brake the aircraft at that rate until the pilot depresses one or both brake pedals, thereby switching to manual control.
A further disadvantage to the above system is that it does not have the capability to provide a pilot with "feel" control of the brakes such that the pilot is assured of having a smooth, linear braking response which is at all times proportional to the displacement of a pilot-operated brake pedal.
As will become apparent upon further reading of this disclosure, the present invention solves the above-discussed disadvantages.
The following patents disclose other braking systems related or similar to those described above but not as pertinent to the present invention:
______________________________________ Amberg et al U.S. Pat. No. 4,078,845 Bissell et al U.S. Pat. No. 3,920,204 DeVlieg U.S. Pat. No. 3,917,356 Shiber U.S. Pat. No. 3,881,783 Bissell et al U.S. Pat. No. 3,847,445 Rouf et al U.S. Pat. No. 3,829,167 Lucien U.S. Pat. No. 3,237,996 Hirzel U.S. Pat. No. 2,992,860 Armstrong et al U.S. Pat. No. 2,944,772 Bricker U.S. Pat. No. 2,764,263 ______________________________________